南海北部天然气水合物沉积环境中自生矿物特征

Characteristics of Authigenic Minerals from the Northern South China Sea

南海北部陆坡发育的自生岩石矿物主要有碳酸盐岩、黄铁矿、石膏等,主要分布在天然气水合物最有潜力的区域,如西沙海槽、神狐海域、东沙西南和东北海域,以东沙东北部海域为自生矿物发育最密集区域。自生碳酸盐岩主要呈结核状、结壳状、烟囱状、块状等产出,神狐海域和东沙西南海域以白云石为主,西沙海槽以文石为主,东沙东北部主要以高镁方解石为主,具有较轻的碳同位素值和较重的氧同位素值;自生黄铁矿主要呈长条状,由草莓状黄铁矿组成,具有较大的硫同位素值,分布较为广泛;自生石膏主要呈球状或者块状,透明自形晶结构,分布在神狐及东沙海域部分站位。南海北部自生矿物的这些特点可为我国水合物勘探提供自生矿物方面的证据。

Authigenic carbonates, pyrite and gypsum were the main minerals associated with cold seeps or gas hydrate in the Xisha Trough, Shenhu areas, southwestern and northeastern of Dongsha from the northern South China Sea. The northeastern Dongsha are the most authigenic minerals-riched area in northern South China Sea. These authigenic carbonates consist of concretions, nodules, chimneys, and massive blocks. Mineralogically, the carbonates in Shenhu and southwest Dongsha samples are dominated by dolomite, and aragonite are mainly composed of the samples from Xisha trough, high-Mg calcite are composed of the samples from northeast Dongsha samples. The carbon and oxygen isotopes of carbonate indicated the low carbon isotopic composition and the high oxygen isotopic composition which are identical to the ones retrieved at cold seeps or gas hydrate sites. The authigenic pyrite are rods and mainly composed of framboids pyrite, it has high δ34S value which may result from anaerobic oxidation of methane in gas hydrate-bearing sediment in a close system. Gypsum are mainly collected from Shenhu and northeast Dongsha, it has spherical or massive morphology, and shows a transparent and euhedral shape. The characteristics of these authigenic minerals in northern South China Sea provided the minerals evidence to the gas hydrate exploration in the future.